Current state of the art for trace detection of explosives, chemical and biological threat agents, and other threat agent signatures often requires physical swipes of surfaces to be collected for further on-site or remote instrumental analysis. Collection and subsequent assays of minute amounts of analytes such as explosive residues from surfaces is a primary method for detection of hidden explosives or discovery of residues on persons who have had contact with explosives. For example, collection of trace residues from surfaces is typically conducted by physically sampling surfaces with cotton or muslin swipe materials and swabs. Muslin is a woven cotton cloth that is a widely used surface sampling material for collection of trace explosives and other analyte samples. Explosives detection depends on the effectiveness of the measurement as well as the collection efficacy. Performance of the sampling material is fundamental to the analytical process upon which the entire detection and decision sequence depends.
Presence of trace explosives on swipes can be analyzed by various instruments. Ion mobility spectrometry (IMS) is a principle method presently employed in the field. Recovery of the analyte from the sampling media can be accomplished by rinsing with solvents or by heating the sampling media to introduce the analyte into the instrument for subsequent assay. IMS enables rapid analysis, has low detection limits for many analytes of interest, has a low operating cost, and requires no sample preparation. Consequently, IMS is one of the most widely used analytical methods for explosives detection throughout the world. However, IMS can produce erroneous results due to its lack of selectivity, susceptibility to interference, as well as nonlinear behaviors including, e.g., sample reproducibility issues, and human error. Thus, improving sample collection and analyte introduction into the IMS (and similar systems) should improve sensitivity; stability, and potentially selectivity, thereby resolving many fundamental problems presently plaguing field-deployed instruments that are tasked with trace detection of organics.
While effective, muslin sampling cloths made of cellulosic fibers are not ideal sampling materials. Cellulose fibers include a range of chemical moieties that result in heterogeneous binding of analytes, which can result in distributed or incomplete analyte release. Further, unprocessed muslin sampling swabs contain non-cellulosic compounds found in native cellulosic fibers (i.e. waxes, natural oils and starches) as well as sizing agents and lubricants added during and after textile processing. Processes typically, used to remove these impurities in industry such as mechanical scouring, chemical scouring agents, and enzymatic methods can weaken the cellulosic fibers and render them unsuitable for repeated use due to degradation. The decomposition and degradation of an unstable swab material can release contaminants into a detection instrument and therefore interfere with the sample analysis and negatively impact the detection process. Additionally, cellulosic fibers have a limited thermal stability as they decompose at the relatively low temperature of 150° C. And, the high specific heats (>1.3 J/g ° C.) and low thermal conductivity (˜0.24 W/m-K) of cellulosic fiber materials combined with the chemical heterogeneity of the surface result in less than optimal release of analytes from the surface, which can limit the detection performance.
Recently, different materials have been evaluated as candidates for surface sampling including, e.g., raw glass fibers, polytetrafluoroethylene (PTFE) fibers, and aromatic polyamide polymer fibers. These materials have a high thermal stability that allows thermal desorption of an analyte into an IMS. They are also resistant to mechanical and shredding stresses, and offer a high desorption efficiency for several explosive compounds. However, while PTFE has some suitable properties (e.g., is not wetted by water), PTFE has a lower efficiency for collection of explosives than muslin or cotton swabs. And, tests on simple glass fiber materials show they do not retain sufficient structural integrity and degrade during use.
Accordingly new swipe samplers and preparation processes are needed that are physically and thermally stable, enhance analyte adsorption and collection, and provide excellent desorption of analytes for detection, e.g., of explosives and other threat agents. The present invention addresses these needs.